Are Irradiated (Color Enhanced) Diamonds Safe?
As the cost of fancy color diamonds are beyond the reach of many, color enhanced diamonds or irradiated diamonds fill the gap if you have no qualms about radiation. As natural color diamonds are rare, irradiation makes a huge rainbow of diamond colors available. The process begins with exposing a poorly colored diamond to a radioactive treatment, which yields a green or blue-green hue. To produce other colors, the diamonds are further heat treated. Only the outer layers of a diamond are affected by this treatment.
The radioactivity is rendered nearly inert after this treatment, but there is much debate about this process, especially on older diamonds that were irradiated with radium, which can retain levels of radiation similar to that of a watch that was radium painted. Newer irradiation techniques bombard the crystal with atomic particles and leave almost no radioactivity. Some treatments require a "cool down" period required by the Nuclear Regulatory Code (NRC). Despite all this, color enhancements are generally considered benign.
However, if they are exposed to high heat again, the color can change in varying degrees, but it will never return to a colorless state. When you take a color enhanced diamond to be repaired, make sure to inform your repair dealer.
Color Enhanced Diamond Scams
"Overdosed" irradiated diamonds are produced and occasionally imported into the United States. U.S. customs agents or gem labs usually catch them. Disreputable dealers try to scam consumers by polishing off the GIA laser inscribing and try to sell you a "fancy" or "natural" color diamond at a huge discount. However, this can also happen with a piece of jewelry where the stone is already set. The laser inscribing will be there, but you won't be able to see it. To ensure not purchasing these, only deal with reputable dealers. Your average retailer does not deal with color enhanced diamonds, so you must get referrals.
Color enhanced diamonds are considered permanent in that their color will not fade unless exposed to intense heat again. The GIA reports note them as such with HPHT Annealed or Artificially Irradiated and also insists they be laser-inscribed with the same designation. GE (General Electric) develped the HPHT (high-pressure high-temperature) treatment. A diamond that has been heat treated by the GE HPHT process will be inscribed with the symbol GE POL.
While the GIA grades irradiated diamonds, these are not natural colored diamonds and shouldn't be valued as such. Disclosure is always mandatory and if you have any doubts, have your loose stone or jewelry examined by a professional appraiser with a spectro-photometer.